The role of hornification in the disintegration behaviour of TEMPO-oxidized bleached hardwood fibres in a high-shear homogenizer

The effect of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation on the structure of hornified fibres and their disintegration behaviour was studied by a method combining gradual disintegration of the fibre structure in an in-line homogenizer with a chromatographic separation technique. It was seen that hornification prior to TEMPO-mediated oxidation had a notable effect on the disintegration behaviour of bleached cellulose fibres in a high-shear homogenizer and on the properties of the resulting particles. Field-emission scanning electron microscopy imaging of the suspensions and viscosity and transmittance measurements revealed that never-dried oxidized fibres disintegrated into bunches of microfibrils and at higher charge densities into thinner and more individual microfibrils. These microfibrils were obtained from fibres through swelling and ballooning. The hornified fibres were mainly cut into shorter ones as the charge density increased. After reversing the hornification and allowing the fibres to swell further, however, microfibrils were also obtained from this source. The charge threshold for efficient microfibril production from never-dried fibres in the high-shear homogenizer used here was 0.7 mmol/g.     

Properties and treatments of pulps from recycled paper. Part II. Surface properties and crystallinity of fibers and fines

Surface properties of bleached kraft pulps were evaluated before and after recycling, and after a series of chemical treatments designed to improve and/or modify the pulp characteristics. The surface free energy characteristics of the pulps were determined using the Wilhelmy technique, and ESCA and ATR-FTIR methods were used to evaluate the chemical composition of the surfaces of the pulp fibers. In general rather small changes were noted at the fiber surfaces with recycling and chemical treatment. Recycling tended to increase the acid component and decrease the base component of the surface free energy of the pulps. This could result from exposure of carboxyl groups from hemicelluloses and/or from oxidized layers from the bleaching process. ESCA analyses also indicated increased carboxyl concentration at the surfaces of the recycled fibers. Although treatment with aqueous bases and organic solvents tended to increase the hydroxyl content on the surface of recycled pulps, the chemical treatments were not beneficial to pulp quality. AFM and SEM of fiber and fine surfaces of kraft pulps revealed that the fines fraction was altered to a much greater extent with recycling. Although recycled fibers appeared to have improved wettability, these small changes in the surface characteristics do not appear to play the dominant role in the characteristics of recycled pulps. Recycling did not change the crystallinity of whole pulps, but it increased the crystallinity of the fines fraction. The increase in the crystallinity of the fines fraction and the reduction in the water retention value (WRV) and the bulk carboxyl content (xylan) of the recycled pulps, as noted in Part I of this paper, appear to play the predominant role in determining the characteristics of recycled pulps. It appears that the loss of the hemicelluloses in the bulk of the fiber with recycling is much more important for internal fibrillation than the apparent small increase of hemicelluloses at the surface of recycled fibers.     

The effect of electrochemical surface treatments of carbon fibers using scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been applied to the study of the topography of polyacrylonitrile (PAN)-based carbon fibers before and after electrochemical surface treatments. The results show that the electrical anodic oxidation only changes the surface aspects; at nanometric resolution; the nanostructure and nanotexture such as the step-like crystallite stacking are decreased with increasing electric current densities.     

Interactions between cellulose nanofibers and retention systems in flocculation of recycled fibers

Although the positive effect that cellulose nanofibers (CNF) can have on paper strength is known, their effect on flocculation during papermaking is not well understood, and most relevant studies have been carried out in presence of only cationic starch. Flocculation is the key to ensuring retention of fibers, fines, and fillers, and furthermore floc properties have a great influence on paper quality. The aim of this research is to study the interactions between CNF and flocculants by assessing the effect of two types of CNF, from eucalyptus and corn, on the flocculation process induced by three different retention systems [a dual system, polyvinylamine (PVA), and cationic starch as reference]. The results showed that CNF interacted with the flocculants in different ways, affecting flocculation efficiency and floc properties. In general, addition of CNF increased floc stability and minimized overdosing effects. Moreover, presence of CNF increased floc size for given PVA dose; therefore, CNF addition could contribute to improve the wet end in the paper machine if combined with the optimal flocculant and dose.     

Physical properties and application development of recycled products from waste plastics

The degradation of the physical properties of polypropylene (PP) used for automotive outer trims for several years is unexpectedly small. It, therefore, can be fully anticipated that PP so used can be recycled for the same purpose or for other applications.     

Optimization of operating conditions in a high-shear mixer using dem model: determination of optimal fill level

For the purpose of evaluating optimal fill level of starting materials in a high-shear mixer, discrete element method (DEM) simulation was conducted to visualize kinetic status between particles. The simulation results obtained by changing fill levels were used to determine solid fraction of particles, particle velocity, particle velocity vector, and kinetic energy and discuss the flow pattern. Optimal fill level was obtained from the information on these matters. It was pointed out that understanding the kinetic energy between particles in an agitating vessel was effective in determining the optimal fill level. Granulation experiment was conducted to validate the optimal fill level obtained by the simulation, confirming the good agreement between these two results. It was pointed out that determination of kinetic energy between particles through the simulation was effective in obtaining an index of the kinetic status of particles. Further, it was confirmed that the simulation could provide more information than conventional granulation experiments could provide and also helpful in optimizing the operating conditions.     

Renewable resource-based composites of recycled natural fibers and maleated polylactide bioplastic: Characterization and biodegradability

The thermal properties of composite materials composed of polylactide (PLA) and green coconut fiber (GCF) were evaluated. Blends containing maleic anhydride-grafted PLA (PLA-g-MA/GCF) exhibited noticeably superior thermal properties due to greater compatibility between the two components. The dispersion of GCF in the PLA-g-MA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules, between the carboxyl groups of PLA-g-MA and the hydroxyl groups in GCF. In addition, the PLA-g-MA/GCF blend was more easily processed due to a lower melt viscosity. Each composite was subject to biodegradation tests in a Burkholderia cepacia BCRC 14253 compost. The bacterium completely degraded both the PLA and the PLA-g-MA/GCF composite films. Morphological observations indicated severe disruption of the film structure after 9-12 days of incubation. The PLA-g-MA/GCF (10 wt%) films were not only more biodegradable than those made of PLA, but also exhibited lower molecular weight and intrinsic viscosity, implying a strong connection between these characteristics and biodegradability.     

Production of cellulases and xylanases byTrichoderma viride and biological processing of lignocellulose and recycled paper fibers

Applied Biochemistry and Biotechnology - The production of cellulases and xylanases byTrichoderma viride L-333 was studied. Significant amounts of extracellular enzymes were obtained when submerged...     

Co-electrospinning of core-shell fibers using a single-nozzle technique

Co-electrospinning is ideally suited for fabricating continuous fibers encasing materials within a polymer sleeve, but requires relatively complex coannular nozzles. A single-nozzle co-electrospinning technique is demonstrated using blends of poly(methyl methacrylate) (PMMA)/polyacrylonitrile (PAN) solutions in dimethylformamide (DMF). The as-spun fibers have outer diameters in the range of 0.5-5 microm and possess a core-shell structure similar to that attained via coannular nozzles. The technique relies on the precipitation of PMMA solution droplets, which become trapped at the base of the Taylor cone issuing the PAN solution jet from its tip. A theoretical analysis shows that the outer shell flow is sufficiently strong to stretch the inner droplet into the Taylor cone, thus forming a core-shell jet. The method seems attractive for technological applications involving macroscopically long and radially inhomogeneous or hollow nano/micro fibers.     

Molecular weight distribution and mechanical behavior of PBI fibers

Two different polybenzimidazole (PBI) samples have been investigated in order to correlate the differences in molecular weight distribution (MWD) with changes in the elastic modulus and strength of undrawn and drawn fibers. It has been found that within the weight-average molecular weight range (7,000 ≤ M_w ≤ 13,000) there was no obvious correlation with M_w and M_n. However, one sample had a narrow unimodal molecular weight distribution and the other a wide bimodal molecular weight distribution. The small percentage of high molecular weight present in the latter sample gave its fibers better mechanical properties. X-ray diffraction studies showed that the orientation in both drawn fiber samples was equal. This isolated the effects of the molecular weight distribution on mechanical properties.     

Physical and mechanical properties of ultra-oriented high-density polyethylene fibers

Ultra-oriented high-density polyethylene fibers (HDPE) have been prepared by solid-state extrusion over 60–140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x-ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20–30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two-phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x-ray measurements. Solid-state extrusion of HDPE near the ambient melting point produced a c-axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c-axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.     

GDME-based methodology for the determination of free formaldehyde in cosmetics and hygiene products containing formaldehyde releasers

Analytical and Bioanalytical Chemistry - Formaldehyde is often applied in the industrial production of different products, such as textiles, insulation materials, or cosmetics, due to its...     

Properties and treatments of pulps from recycled paper. Part I. Physical and chemical properties of pulps

The mechanical, physical, and chemical properties of recycled pulps were evaluated after a series of treatments designed to improve and/or modify the pulp characteristics. Tensile strength, bursting strength, and apparent density of the pulps decreased with recycling. However, the tear strength, in most cases, increased after the first recycle and then decreased after the second recycle. Carboxyl content and WRV of pulps also decreased with recycling. Chemical treatments did not increase the bonding ability of recycled pulps and, in most cases, decreased the physical properties of the pulps. Altering the physical state of the cellulose microstructure through additional swelling did not appear to be a significant factor for strength restoration. It may be that the hemicelluloses plan a greater role in recycling than originally thought.     

Preparation and physicochemical and mechanical properties of low-substituted cellulose phosphate fibers

Mechanical and physicochemical properties of cotton and viscose fibers esterified with aqueous solutions containing orthophosphoric acid and urea in different ratios were studied.     

Interaction of microcrystalline cellulose and water in granules prepared by a high-shear mixer

Microcrystalline cellulose (MCC) granules were prepared by wet granulation using a high-shear mixer. Physical characteristics of the granules were investigated using near IR spectrometry, thermogravimetry and isothermal water vapor adsorption. Near IR spectra of dried MCC granules prepared for various granulation times exhibited different peak intensities at 1428, 1772, and 1920 nm, which were assigned to functional groups of cellulose or water. On isothermogravimetric analysis, the rate of dehydration of water was shown to decrease with granulation time. These results suggest that the physical structure of MCC could change during the granulation process, and the interaction between MCC and water was gradually strengthened. The isothermal water vapor adsorption curves suggested that the amorphous region of MCC would be divided by the strong shear force of the impeller, because the high adsorption ability of intact MCC in the low humidity region was diminished in granules collected following 5 and 10 min of granulation. It was suggested that MCC formed a network which caught water within its structure during the wet granulation process.     

Characterization of recycled polyamide 6: Effect of polypropylene and inorganic contaminants on mechanical properties

Recycled polyamide 6 (PA6) from post-industrial waste fibers (PIW) and post-consumer carpet waste (PCW) are characterized in this study. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) indicate the presence of polypropylene (PP) in PCW. Furthermore, measured ash content of PCW is ca. 6 wt.%, while PIW has only 0.5 wt.% inorganic content. X-ray fluorescence (XRF) and X-ray diffraction (XRD) show that inorganic contaminants of PCW and PIW are calcium carbonate (CaCO₃) and titanium dioxide (TiO₂), respectively. Due to higher inorganic filler content, PCW exhibits higher melt viscosity and higher storage modulus than that of PIW. PIW has 20% higher tensile strength than that of PCW. However, a drastic 70% drop is observed in vibration weld strength of PCW, which is attributed to its PP contamination. The negative effect of PP on the weld strength of recycled PA6 is also confirmed by measuring the mechanical properties of model compounds.     

Determination of radiolysis products in gamma-irradiated multilayer barrier food packaging films containing a middle layer of recycled LDPE

Volatile and non-volatile radiolysis products and sensory changes of five-layer food packaging films have been determined after gamma irradiation (5–60 kGy). Barrier films were based on polyamide (PA) and low-density polyethylene (LDPE). Each film contained a middle buried layer of recycled LDPE or 100% virgin LDPE (control samples). Data showed that a large number of radiolysis products were produced such as hydrocarbons, alcohols, carbonyl compounds, carboxylic acid. These compounds were detected in the food simulant after contact with all films even at the lower absorbed doses of 5 and 10 kGy. The type and concentration of radiolysis products increased progressively with radiation dose, while no new compounds were detected as a result of the presence of recycled LDPE. In addition, irradiation dose appears to influence the sensory properties of table water in contact with films.